A number of industrial processes are based upon the electrolysis of aqueous salt solutions. Among the most important of these is the electrolysis of alkali metal chlorides to produce the corresponding alkali metal hydroxide and chlorine, or the corresponding alkali metal chlorate. Of the alkali metal chlorides, sodium chloride is the most abundant and is most utilized.
One widely employed method of electrolysis is the utilization of a cell having separate anode and cathode compartments. The compartments are separated by a porous separator. For some years, such cells utilized a separator of fibrous asbestos. More recently with the advent of metal, or dimensionally stable, anodes, permselective separators, such as fluorocarbon resin modified asbestos mixtures, have substantially replaced asbestos as the separator component. Such cells typically have a conductive base in which the anode members, generally flat blades, are vertically positioned. The base is separated from the interior of the cell compartment by a cover, or blanket, of elastomeric material. Typically, anode members are flanged and are inserted through perforations in the blanket and into electrical contact with the base. The base portions of the anode members are usually threaded to accept a metallic, usually copper, stud which extends through said base and be fixedly attached thereto, e.g., with a nut. In any case, the arrangement allows the base portion to be electrically attached to the anode members and separated from the remainder of the cell compartment.
In use, electrolytic cells are operated on a continuous basis, that is, the process is operated until one of the cell components requires replacement. For example, the separator may be required to be replaced because of clogging or leakage, the anodes because of wear, or the blanket because of leakage. Thus, it is important to utilize cell components which have a long life under cell operating conditions. As one component is improved, development work concentrates on the next most weak component.
Previously elastomeric blankets have been fabricated of neoprene rubber, EPDM compositions or various blends of natural and synthetic rubbers. U.S. Pat. Nos. 3,794,577 and 3,857,775 recite examples. However, none of these materials has proved totally satisfactory in actual use. Although each variation has lengthened the life of the blanket, the improvements in blanket life have not been sufficient to provide a blanket which would have a longer life than the other cell components.
The present invention provides a cell having a cell blanket with an extraordinary life when utilized in the hostile operating conditions of an electrolytic cell. Further, the present cell blanket has a substantially improved shelf life as compared to conventional blankets. Conventional vulcanized blankets tend to shrink over time and, because of the exacting fit required, must be fabricated and installed prior to such shrinkage. The present cell blankets are substantially dimensionally stable and may be fabricated and stored for time periods not previously attained by prior art blankets.
The present blankets also exhibit a substantial improvement in the compression set of the blanket. Compression set is a measure of the ability of the blanket to return to its original dimensions after compression. Such improvement facilitates a tight, sure seal between the base member and the portion of the anode members positioned in the operating portion of the cell.